Few subjects more predictably animate furious disagreement and cross-purposes discussion than the origins of human warfare. Are people “naturally” belligerent? And what does that even mean?

The question taps a deep old well of ideological intuition. Were the lives of our ancestors, as Thomas Hobbes' infamously put it in the 17th century, “nasty, brutish and short”? Or, were our ancestors more like the “noble savages” of romantic primitivism? Our beliefs about these issues colour whether we feel our lives are generally better or worse than those of our ancestors.

This dichotomy, in more nuanced forms, has haunted and at times paralysed anthropology since at least the 19th Century. And it reared its head again recently with the divisive reception granted to books such as Steven Pinker’s The Better Angels of our Nature, and Jared Diamond’s The World Until Yesterday, as well as a flurry of renewedinterest in controversial anthropologist Napoleon Chagnon.

Steven Pinker outlines his case that violence has steadily declined throughout history

But the overall battle over the decline of violence is but one theme in the history of violence, a history replete with intriguing sub-plots. The prevalence of warfare among mobile forager band societies occupies a place of particular controversy among anthropologists who actually work in the field.

Until 10,000 years ago, the ancestors of everybody alive today lived in small nomadic bands and foraged what food they could catch or gather. Most of our species' recent past - hundreds of thousands of years - was spent hunting, gathering and moving about in this way. As a result, accounts of human adaptation often consider in some depth this period, given its importance in determining which genes and traits our ancestors bequeathed to us.

A small number of “mobile forager band” (MFB) societies still exist - or persisted long enough for anthropologists to study them systematically. It is from these peoples that we draw almost everything we know about the way our ancestors lived until the seismic changes wrought by agriculture.

From modern accounts of MFB societies we can infer that our ancestors were certainly violent. Ethnographies document homicidal personal disputes, spousal killings, fights among men over women, executions of outsiders and inter-group killings.

But were our MFB ancestors war-faring? War, here, is a subset of lethal violence that involves members of a group working together to overcome members of other groups. It’s one of those appalling human traits that romantics would like to pretend doesn’t happen elsewhere in the animal world. But ants, by this definition, certainly wage war among colonies. And Jane Goodall’s discovery in the early 1970s that chimpanzees from one group occasionally work together to kill members of other groups suggests our closest living relatives look pretty war-like too.

Harvard Anthropologists Richard Wrangham and Luke Glowacki argued in a recent paper that our ancestors waged chimp-like warfare, launching coordinated surprise attacks on other groups. Raids of this sort, in order to weaken other groups, or capture livestock, property or women, are a feature of every society that has domesticated livestock, horses or agricultural crops. But these societies tend to involve bigger, more complex groups, and forms of wealth more worth fighting over than MFB societies.

Mobile forager bands have more characteristically egalitarian political structures, less coalition-forming behaviour, and few resources or possessions worth defending. These properties don’t make good ingredients for war-mongering. So it’s really worth knowing just how much of MFB violence can be considered warfare. As my post-doc advisor was occasionally heard to say:

Just get the data!

Last week’s edition of Science contained an exhaustive analysis by Douglas P. Fry and Patrik Söderberg, who scrutinised the existing accounts of all lethal violence in 21 MFB societies. They tabulated the causes of 148 cases of lethal aggression, and found that two thirds originated from within-group conflicts. The majority of these deaths were caused by a lone perpetrator.

Only one third of events could possibly be construed as acts of warfare. And most of these events occurred in one society - the Tiwi of northern Australia in which ethnographers documented several intergroup disputes and revenge-seeking cycles. In the other 20 MFB societies only around 15% of deaths by lethal aggression could possibly fit the definition of war.

The authors concluded that:

most incidents of lethal aggression among MFBS may be classified as homicides, a few others as feuds, and a minority as war.

Refreshing as it is to see a calm, data-driven approach to answering a tightly-proscribed research question, the prevailing discussion over the last week has fallen into old ruts.

“War arose recently” proclaimed ScienceNews. Fair enough. I don’t think Fry and Söderberg would contest the argument that agriculture and the rise of complex societies made war a worthwhile - in the economic sense rational - option. And that stoked the body count.

But the Socialist Worker led, as it does, the charge against scientific accounts of human nature. War Not Due to Human Nature it proclaimed, reeling off a link-fest of SW diatribes against scientific accounts of human behaviour, and then linking to a somewhat more considered piece from Slate.

I’m happy to grant that these data show that MFB societies don’t make as much war as agriculturalists and pastoralists, not to mention contemporary weapon-rich societies. But I’m intrigued about the Tiwi, who don’t fit the mould. I’m not familiar with the data, but according to ScienceNews, Samuel Bowles reckons the Tiwi were among the more peaceful hunter-gatherer societies he studied in an earlier Science paper that reached more bleak conclusions about the history of war.

And I’m equally intrigued by how societies can tip so quickly into belligerence as soon as they settle down and accumulate some wealth. The capacity to form coalitions and deploy them for ill may have been there all along.